sql server - Use transactions for select statements?

Question

I don't use Stored procedures very often and was wondering if it made sense to wrap my select queries in a transaction.

My procedure has three simple select queries, two of which use the returned value of the first.

Answer 1

In a highly concurrent application it could (theoretically) happen that data you've read in the first select is modified before the other selects are executed.

If that is a situation that could occur in your application you should use a transaction to wrap your selects. Make sure you pick the correct isolation level though, not all transaction types guarantee consistent reads.

Update : You may also find this article on concurrent update/insert solutions (aka upsert) interesting. It puts several common methods of upsert to the test to see what method actually guarantees data is not modified between a select and the next statement. The results are, well, shocking I'd say.